For displaying high information content images in conventional display technologies, a plurality of pixels is organized into an array of addressable columns and rows. For a color display, each pixel is organized into a cluster of sub-pixels, each individually activated to form a desired color. The pixels are activated in a predetermined manner to generate an image. Color can also be generated by sequentially activating the various colors, for example from three light sources, and integrating those colors over time.
Consider for example a digitized image representing a full-color detailed map of a major metropolitan area. To store the digital information necessary to display such a map could require several gigabytes of memory. At present, the only convenient and economical way to store memory of such a quantity is to use CD-ROM technology. To form a display using conventional technology, the data would be read from the CD-ROM and used to activate the pixels in a predetermined manner.
If the information changes, the memory must correspondingly change to display an accurate image. For the example of the metropolitan map discussed above, to be useful in a driving situation, the map would preferably include information such as the location of traffic problems, road construction, public activities that would impede traffic and the like. Because CD-ROMs cannot be changed once written, a substitute CD-ROM must be provided. Unfortunately, traffic conditions change too often for such a system to be useful. What is needed is a display system that allows for mass storage of digital information that can be readily altered. Substituting memory for the CD-ROM technology would allow alterability of the displayed image but would dramatically increase the cost of such a system.
In one display technology grating light valves can selectively diffract an incident beam of light. A variety of known grating light valves are discussed in the prior art and some others are or were commercially available. One grating light valve is described in U.S. Pat. No. 5,311,360. A similar grating light valve and a method of making it are described in two U.S. patent applications, Ser. No. 08/482,188 entitled: FLAT DIFFRACTION GRATING LIGHT VALVE, now U.S. Pat. No. 5,841,579 and Ser. No. 08/480,459 entitled: A METHOD OF MAKING AND AN APPARATUS FOR A FLAT DIFFRACTION GRATING LIGHT VALVE, now U.S. Pat. No. 5,661,592 both filed on Jun. 7, 1995. Each of these three patent documents is incorporated herein by reference. The discussion that follows is in no way intended to modify or alter the scope of the teachings or claims of any of the above three captioned references. Rather, this discussion is intended only to schematically describe these references insofar as it will aid in understanding the present invention by providing bases for comparing or contrasting those technologies to the present invention. The technology disclosed in these three patent documents is generically referred to herein as grating light valve (GLV) technology.
According to the teachings of these three references, a diffraction grating light valve is formed of substantially parallel ribbon structures. The ribbons are formed over a semiconductor substrate using certain conventional semiconductor processing steps such as those used for forming integrated circuits as will as other steps. FIG. 1 shows the grating light valve 10 from the U.S. Pat. No. 5,311,360. Each of the ribbons 18 have an upper surface coated with a reflective material 20, such as aluminum. In the spaces between the ribbons, the substrate 16 is also coated with the reflective material 24. The height difference between the reflective material 20 on the ribbons 18 and the reflective material 24 on the surface of the substrate 16 is 1/2 the wavelength .lambda. of an expected beam of light. Because of this height difference, the beam of light reflects from the surface of the grating light valve essentially as if it were a specular mirror as shown in FIG. 2.
Upon applying a predetermined voltage potential across the ribbons 18 and the substrate 16, the ribbons 18 are caused to deflect downwards and contact the substrate 16. The grating light valve 10 is constructed so that the height difference in this deflected state is 1/4 the wavelength .lambda. of the expected beam of light. Because of this height difference, the beam of light is diffracted at the surface of the grating light valve essentially as shown in FIG. 3.
FIG. 4 shows a cross section view of two adjacent ribbons according to the technology taught in the two above captioned patent applications in an undeflected and reflecting state. According to the applications, in an undeflected state all the ribbons are in an up position. All the reflecting surfaces are on ribbons rather than having alternate ones of the reflectors mounted on the substrate as in U.S. Pat. No. 5,311,360. The ribbons are selectively deformable by coupling the ribbons to external control circuitry. When the ribbons for a single grating light valve are all in an up position, an essentially flat specular mirror is presented to an incident beam of light. The mirror is necessarily broken by the gaps between the ribbons of a single grating light valve structure.
FIG. 5 shows a cross section view of two adjacent ribbons in a deflected and diffracting state. Alternate ones of the ribbons within a single grating light valve are selectively deformed and deflected into contact with the underlying substrate. When this occurs, the grating light valve diffracts the incident beam of light.
For the technologies described above, a voltage is coupled to the selected ribbon or ribbons and to the substrate (or an appropriate conductor mounted on the substrate) for effecting the deflection of one or more ribbons in a predetermined manner. An incident beam of light that strikes such deflected ribbons will form a diffracted beam. It will be understood that the light from the diffracted beam is collected at the diffracting angle. Thus, no light is collected and accordingly there is no or low intensity when the ribbons are not deflected and thus the grating light valve is acting as a specular mirror. When the ribbons are deflected, the incident beam of light is diffracted to the collection point and the collected intensity is large. To form an image using any of the grating light valve technologies discussed above, or those in the prior art require a source of digital memory for selectively controlling a display state in each pixel.